1. Field
The present disclosure relates to a molding element obtained by sintering and comprising particular venting means. The molding element is intended to be arranged in a tire mold, notably a mold of the segmented type.
2. Description of Related Art
A segmented mold comprises several separate parts which, when brought relatively closer together, delimit a molding space of toroidal overall shape. In particular, a segmented mold comprises two lateral shells for molding the sidewalls of the tire and several peripheral segments situated between the shells for molding the tread of the tire. All of these parts are brought closer together with suitable dynamics thanks to a determined mechanism.
In order to mold the tread, the mold segments comprise molding elements. What is meant by a molding element is an element of the mold which comprises a molding surface that allows part of the tread of a tire to be molded.
It is possible to create a molding element using a selective fusion method more commonly referred to as sintering. This method uses a beam of energy to fuse a metallic powder. A “beam of energy” means electromagnetic radiation (for example a laser beam) or a beam of particles (for example an electron beam).
A sintering method using a laser, hereinafter referred to as a laser sintering method, is known from document EP1641580. In that document, a first layer of metallic powder is spread on a plate. All or some of the particles of this first layer of powder are then agglomerated by the beam of a laser according to the shape of the object that is to be obtained. Once this step has been performed, a second layer of powder is spread on the first layer of powder so that it in turn can be selectively fused using the laser. By repeating these operations of spreading the layer and fusing using a laser, a sintered object is built up layer by layer.
Document WO2010/076502 discloses a particular molding element obtained using this laser sintering technique. This molding element, referred to as a skin, is of small thickness and is intended to be placed in a mold. In order to avoid air being trapped between the mold and a green tire during an operation of vulcanizing this tire, it is necessary to provide venting means in the molding element.
Documents DE102004028462 and DE102004052766 disclose examples of such venting means. More particularly, these documents disclose a mold part comprising a molding element obtained by laser sintering and an interface element interfacing with the rest of the mold. This interface element is not sintered and is secured to the molding element. The molding element throughout its volume comprises a plurality of pores forming small-sized cavities. These cavities are able to guide the air towards drillings formed in the interface element and opening to the rear of this interface element. However, the presence of a high number of pores in the molding element reduces the material density of this element and makes it more fragile to mechanical loading. Thus, the venting solutions disclosed in documents DE102004028462 and DE102004052766, if applied to the molding element of document WO2010/076502, would make the latter element too fragile because of its small thickness. Furthermore, in documents DE102004028462 and DE102004052766, it is necessary to provide an additional operation of making a hole in the interface element.
Document DE19628166 discloses another venting solution in which provision is made for an insert to be attached in a hole produced beforehand within the depth of the molding element. The insert comprises a hollow cylindrical body and a platelike head formed as an integral part of this body. The head comprises a plurality of holes opening into the hollow part of the cylindrical body. The depth of the holes is limited to the thickness of the plate so as to reduce the risks of these holes becoming fouled and to encourage the removal of air via the hollow body of the insert. The use of an insert attached into the molding element does, however, make this solution complex and costly.
There is therefore a need to offer a simple and economical venting solution for a molding element of a tire mold.